3-(hexadecyloxy)propyl hydrogen ((R)-1-(6-amino-9H-purin 9-yl) propan-2-yloxy)methylphosphonate; (referred to as CMX157, hexadecyloxypropyl tenofovir or HDP-TFV), a lipid conjugate of tenofovir, was designed to mimic lysophosphatidylcholine to take advantage of natural lipid uptake pathways and to achieve high intracellular concentrations of the active antiviral, with the aim of increasing the effectiveness of tenofovir (TFV) against wild-type and mutant HIV (See Hostetler et al. Enhanced oral absorption and antiviral activity of 1-O-octadecyl-sn-glycero-3-phospho-acyclovir and related compounds in hepatitis B virus infection, in vitro. Biochem Pharmacol 53:1815-22 (1997); Painter et al., Antimicrob. Agents Chemother. 51:3505-9 (2007), and Painter, et al., Trends Biotechnol. 22:423-7 (2004).) In addition, CMX157 may also be used to treat HIV and/or HBV and inhibit the development of resistance to other antiviral compounds. (See PCT Publication Nos. WO 2009/094191 and WO 2009/094190). The structure of CMX157 is shown below:

Recent data have indicated that the gammaretrovirus xenotropic murine leukemia virus-related virus (XMRV) and other murine leukemia virus (MLV)-related viruses are associated with prostate cancer and/or chronic fatigue syndrome. (See for example, Schlaberg R et al., PNAS, 106 (38): 6351-6 (2009), and Lombardi V C, et al., Detection of an infectious retrovirus, XMRV, in blood cells of patients with chronic fatigue syndrome, Science, 326 (5952): 585-9, (October 2009), and Lo et al., PNAS early edition, published online before print Aug. 23, 2010, doi: 10.1073/pnas.1006901107). So far, there is limited medical treatment for prostate cancer and there is no effective treatment for chronic fatigue syndrome. Therefore, there is a need for new drugs that can be used to treat viral diseases.